A.
individual bargaining. Although George asked the union for the increase in wages, they asked everyone else as well.
B.
threaten to go on a strike . There is no threat here.
C.
collective bargaining . Yes, they go on to do something for the group.
D.
threaten to quit their jobs . No mention of this in the reading section.
E.
filing a petition to the government. No mention of government anywhere.
The answer is going to be C, collective bargaining .
I hope this helps! :)